Apparatus for painting tubular surfaces



Oct. 22, 1963 n. E. GRlEsEMER ETAL 3,108,023

APPARATUS FOR PAINTING TUBULAR SURFACES Filed March 1. 1961 UnitedStates Patent O 3,108,023 APPARATUS EUR PAENTHNG TUBULAR SURFACESDouglas E. Griesemer and Morris R. Weingarten, L ancaster, Fa.,assignors to Radio Corporation 'of America,

a corporation of Delaware Filed Mar. 1, 1961, Ser. No. 92,559 8 Claims.(Cl. 118-215) 'Ihis invention relates to apparatus for painting orcoating cylindrical surfaces and particularly to apparatus for paintinga spiral stripecoating or coatings on 1an internal conically-shapedsurface of the tubular wall of a cathode ray tube bulb. l

One type of cathode ray oscillograph tube, which has a bulb including afaceplate, a neck, and an interconnecting conical funnel section, isprovided with a spiral strlpe of conductive paint (coating material) onthe internal surface of the funnel. ln operation of the tube, anelectrical potential is applied to the ends of the spiral 'str1pe toproduce a gradient .electrostatic field longitudmally along the funnelsection of the tube. Accordingly, the spiral stripe must be electricallycontinuous, and none of the turns of the spiral should be shorted out.Discontinuities, if present, prevent current flow along the spiralstripe and thus prevent generation o-f the desired gradientelectrostatic field. Electrical shorts between turns o-f the spiral, ifpresent, result in nonuni-formities of the desired gradientelectrostatic field.

A device for painting the spiral stripe on the internal surface of thetunnel may include a paint applicator which is inserted into the funnelin contact with the internal surface thereof. The funnel and the coatingdevice may then be rotated and moved longitudinally relative to eachother so that the paint applicator traverses the desired spiral path onthe bulb. However, some difficulties are encountered in painting thespiral since the surface to be painted varies in circumference along thelongitudinal axis thereof. If uniformity oi the stripe is to beachieved, theV amount of paint applied per lineal unit length of thestripe must be maintained constant. This may be done either bycontinuously varying the rate of feeding of the conductive paint to theapplicator, or continuously varying both the rotational and axialadvance speeds or the apparatus. Prior ant apparatuses for achievingeither of these two alternatives for maintaining uniformity of thespiral stripe have, at the best, been complex and costly.

It is'therefore an object of my invention to provide a new and improvedapparatus ifor painting cylindrical surfaces and particularly a new andimproved apparatus for painting spiral stripe conductive coatings on theinternal surface of funnel-shaped cathode ray tube bulbs.

lt is a further object of my invention to provide a simple andinexpensive apparatus which will apply spiral stripe coatings oninternal conical surfaces and which in so doing will automaticallymaintain constant the amount of coating material applied per lineal unitlength of the stripe.

Briefly, apparatus accordi-ng to my invention comprises a pair ofrollers rotationally coupled to each other, as for example by beingfixed to a common shaft. The rollers are supported at the end of an armwhich is extendable into a cathode ray tube bulb to position theperipheries of the two rollers in contact with the internal surface tobe painted. Upon rotation and longitudinal advance of the bulb relativeto the rollers, one roller is rotatably driven by its frictional contactwith the surface and thus acts as a drive for the other roller whichcontinuously dips into a paint-filled well and applies the paint -to thebulb surface in a spiral stripe.

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ln the drawings:

FIG. 1 is lan elevation View of apparatus according to the inventionshowing its application to a work piece in the form of a cathode raytube envelope; and

FIG. 2 is an enlarged perspective view of a portion of the apparatus ofFIG. 1.

Painting apparatus according to the invention may be attached to aconventional machine lathe -for the purpose of painting spiral str-ipecoatings on an internal surface of a cathode ray tube bulb. Thus, inFIG. 1 only those portions of the lathe which are necessary to anunderstanding of the invention :are shown. These lathe portions includea chuck 12 adapted to be rotatably mounted on the head stock of thelathe and a carriage 14 adapted to be moved toward and away from thechuck 12 by the lead screw of the lathe.

In operation, a cathode ray tube bulb 16 to be painted is mounted in thechuck 1 2 Afor rotation about its longitudinal axis 18, and the paintingapparatus 10 according to the invention is mounted on the carriage 14lfor extension into the bulb 16. The painting apparatus x10 may forexample be mounted as shown on a lathe tool post 20 xed to the carriage'14.

The painting apparatus 10 comprises a bracket 22 which vis fixed, as bybolts to the lathe tool post 20. An arm 24 is pivotalfly mounted betweenits ends on the bracket 22 near the Ifree end thereof by a horizontalpin 26. The arm 24 4is oriented to extend `generally parallel to thebracket 22 so that it may be extended along withl the bracket into thebulb 16 through a neck section 30 thereof. A paint applicator 312 is`pivotally mounted on a yoke 34, which is in turn mounted on the supportarm 24 near one end thereof. Bias means is provided for rotatably urgingthe arm 24 about its pivot 26 to press applicator l32 upward and againstthe internal conical surface `35 of the bulb lo. One simple fform ofthis means may comprise a Weight 36 hung from the other end of thesupport arm 24. Other alternative means, such as a spring loading of thesupport arml 24, for urging the applicator 32 into contact with the bulbsurface 3S can be used.

FIG. 2 illustrates the details of the paint applicator 32 and its yokesupport 34. The applicator 32 comprises a support member or block 37through which a shaft 38 is rotatably mounted. A tracking or driverolier 40 is fixed 'to the shaft 38 on one side of the support block 37and a paint, i.e. applicator, roller` 42 is fixed to the shaft 38 on theopposite side of the support block 37. The two rollers 40 and 42 arethus rotatably coupled together and are preferably closely spaced toeach other. Collars 44 (only one of which is shown) are fixed to theends of the shaft 38 to retain the rollers 40 4and 42 thereon. The shaft38 is so disposed relative to the support block 37, and the rollers 401and 42 are of such size, that both rollers extend slightly above onesurface 46 'of the support block 37 so that they may peripherallycontactthe surface 35 to be painted.

A housing member 48 having three sides and a bottom is secured to thesupport block 37 to partially enclose the paint roller 42. The housing`48 in combination with the end wall `S0 of the support block A37 thusprovides a paint tank .52. When the paint tank 52 is lled or partiallyilled with a suitable paint, the painting roller 42 will extend orcontinuously dip into the paint. Y

In la preferred embodiment of the applicator 32, both the drive roller40' and paint roller 42 are provided with peripheral bands or Itires 53and 54, respectively, of a desired material. For example, since thedrive wheel 40 should make good frictional gripping contact with theinternal bulb surface 35, its band 53 is preferably of a material suchas rubber. The band 54 on the paint roller is of a material mostsuitable for picking up and apply- 3 ing paint to the surface 35. Thepaint roller band 54 may be of a material such as felt, nylon, orleather. Alternatively, the paint roller band 54 may be omitted and theperipheral surface of the paint roller -42 knurled.

The yoke 34, which supports the applicator 32 on the arm 24, comprises apair of generally L-shaped members 60. The two L-shaped members 60` aresecured to the end of the support arm 24 by a bolt 62. The support block37 is pivotally supported between the L-arms 60 at their ends by screws66 (only one of Iwhich is shown) fastened to the support block 37. Thesupport block 37 is preferably provided with slot-like recesses 68 atthe sides thereof into which the L-arms 6) are disposed. The recesses 68are of a sufficient depth and width to receive the L-arms 6G so thatthey do not extend beyond the ends of the support block 36. Thisminimizes the overall size of the applicator 32 and its mounting means34, thus permitting it to be inserted into a smaller bulb neck thanwould otherwise be possible.

In the operation of the painting apparatus 10, the tank 52 is filledwith a paint suitable for application to the bulb surface 35. Such apaint may, for example, comprise the ordinary conductive coating paintknown in the industry as aquadag. With the 'bulb 16 mounted in the chuck12, and the painting apparatus mounted on the carriage 14, theapplicator 32 is then inserted into the bulb as shown in FIG. 1. Thedrive roller 4Q is thus pressed into frictional rolling contact with thebulb surface 35 by the force of the weight 36. The drive of the lathe isrthen engaged so as to rotate the bul-b 16 and axially advance thecarriage 14 to move the applicator 32 in a direction toward the bulbneck 30. The drive roller is frictionally rotatably driven by virtue ofits trolling contact with the rotating bulb surface 35. The paintingroller 42, being coupled to the drive roller 49 is thus also rotatablydriven. Rotation of the paint roller 42 causes it to pick up paint fromthe tank 52, and apply it to the bulb surface 35.

The amount of paint per unit stripe length applied to the surface 35 isautomatically maintained constant since the amount of paint picked up isdependent on the rotary speed of the paint roller 42 which is in turndependent upon the lineal length of the rolling contact of the driveroller 40. By properly adjusting the rotary speed of the bulb 16 and theaxial movement of the carriage 14, a spiral stripe 69 of desired pitchis automatically applied to the bulb surface 35. The pivotal mounting ofthe applicator 32 on the ends of the yoke arms 64 permits the tworollers 40 and 42 to maintain peripheral contact with the bulb surface35 even though :the slope of the surface 35 relative to the axis 18varies, and even though the diameters of the two rollers are differentas hereinafter more fully described.

The amount of paint necessary to paint the desired stripe in some bulbsmay be suitably contained in the tank 52. On the other hand, it may bedesirable to feed additional paint to the tank 52 during the painting ofthe spiral. Furthermore, it may be desirable to maintain a uniform levelof paint in the well 52. In order to continuously feed paint to the tank52, an optional feature of the invention may be provided. This optionalfeature as shown in FIG. 2 comprises a small flexible tube 7)cornmunicating with the tank 52 and extending out of the bulb 16 along.the arm 24 and bracket 22. If desired, a pair of tubes 70 may beprovided so that paint may be continuously circulated into and out ofthe tank 48 during the painting of the bulb surface 35.

The invention has been described in terms of painting a spiral stripewith spaced turns. However, a continuous complete coverage of thesurface 35 may be obtained by adjusting the pitch of the spiraltraversed by the applicator 32 so that one turn of the spiral iscontiguous with or overlaps the adjacent turns. The width of thepainting roller 42 may be increased so as to facilitate this mode ofoperation.

The diameters of the drive roller 4t) and the paint roller 42 need notbe equal. In some cases it may be desirable to make the drive roller 40,for example, smaller than the paint roller 42 so that the paint rollerwill have a greater peripheral speed than that which would providerolling contact between the paint roller 42 and bulb surface 35. Thepaint roller 42 will thus have a sliding relationship, faster or sloweras desired, with the bulb surface 35 and will pick up and apply agreater or less amount of paint than would be the case if exact rollingcontact existed. Such an embodiment of the apparatus 1? might beparticularly desirable if the bulb surface 35 is soiled with foreignmaterials, such as the organic lacquer normally used as a preparatorysurface for aluminization of the phosphor screens of cathode ray tubebulbs. A skidding application of paint by the paint roller 42 might tendto abrade soiled areas and thus force an adherence of the paint theretowhere it would otherwise not adhere.

Since, according to the invention, a separate drive roller 40 is used toprovide the rotation for the paint roller 42, and since the drive roller40 can be positioned to precede the paint roller 42 along the spiralpath, the drive roller never becomes wet with paint. By thus remainingdry, good frictional nonsiip contact of the drive roller with the bulbsurface, and thus uniform driving of the paint roller, is assured. Thiswould not be the case if a single roller were used for both providingdrive and applying paint. Furthermore, the use of separate drive andpaint rollers makes it possible to drive the paint roller at aperipheral speed other than that of rolling contact. The modificationproviding this feature and the advantages thereof are described in thepreceding paragraph.

What is claimed is:

1. Apparatus for coating a cylindrical surface of a work piececomprising rotatable means on which said work piece can be mounted forrotation about the axis of said cylindrical surface, means movablerectilinearly parallel to said axis, an elongated support pivotallymounted on said movable means with one end thereof extendable axiallyalong said cylindrical surface when said work piece is mounted on saidrotatable means, a paint applicator pivotally mounted on said elongatedsupport adjacent said one end thereof, said paint applicator comprisinga drive roller and a paint roller rotatably coupled together anddisposed to make peripheral contact with said tubular surface, and meansfor supplying paint to said paint roller.

2. Apparatus for painting a spiral stripe on the internal tubularsurface of a cathode ray tube bulb, said apparatus comprising: rotatablemeans for supporting a cathode ray tube bulb for rotation about itslongitudinal axis; advance means movable in a direction generallyparallel to said longitudinal axis; a paint roller supported from saidadvance means and extendable into said bulb into peripheral contactingrelationship with said internal tubular surface, means urging saidroller against said internal surface into said contacting relationship,means for supplying paint to said roller, means for rotating saidrotatable means and longitudinally advancing said advance means to causesaid roller means to traverse a spiral path on said internal tubularsurface, and drive means other than said roller coupled between saidroller and said internal surface for controllably rotating said rollerat speeds such that the peripheral speeds of said roller and the ratesof traversal of said spiral path by said roller are maintained at asubstantially constant ratio.

3. Apparatus adaptable for mounting on the carriage of a lathe forpainting spiral stripe coatings on the internal conical surfaces ofcathode ray tube bulbs, said apparatus comprising a bracket adapted tobe mounted on said carriage, an arm pivotally mounted on said bracketabout a given axis, a support member pivotally mounted on said armadjacent an end thereof about an axis parallel to said given axis, adrive roller and a paint roller rotatably coupled to each other androtatably mounted on said support member fwith their axes parallel andso disposed that both of said rollers can simultaneously make peripheralcontact with said internal conical surface to be painted, and a painttank mounted on said support member and so disposed that said paintroller extends thereinto.

4. Apparatus for painting a spiral stripe coating on the surface of atubular member, said apparatus, when oriented in :operating disposition,comprising a bracket, a support arm pivotally mounted on said bracketabout a rst horizontal axis, a paint applicator mounted on said armadjacent one end thereof, and means pivotally urging said arm about saidrst horizontal axis in a direction to move said pain-t applicatorupwardly, said paint applicator comprising a support block pivotallymounted on said arm about a second horizontal axis, a shaft rotatablymounted in said support block on a third axis movable in a planeperpendicular to said second axis when said support block is rotatedabout said second axis, a drive roller and a paint roller fixed to saidshaft, and an open top paint tank mounted on said support member withsaid paint roller disposed partly therein and extending out through thetop opening thereof.

5. Apparatus according to claim 4 and wherein said paint roller is oflarger diameter than said drive roller.

6. Apparatus according to claim 4 and including a paint feed tubeconnected' to said paint tank and extending therefrom back along saidarm whereby said tube can be connected to a reservoir of paint tocontinuously feed paint to said tank during a painting operation of saidapparatus.

7. Apparatus for applying a coating to a surface of a work piece whilesaid work piece is being rotated, comprising a means for supporting androtating said work piece, a movable supporting member movable parallelto the axis of rotation of said work piece, an elongated support memberpivotally mounted on said movable means, an applicator pivotally mountedon said elongated support at one end thereof, said applicator comprisinga drive roller and an applicator roller rotatably coupled together andadapted to make peripheral contact with the surface of said work piece,and means for supplying a coating material to said applicator roller.

8. Apparatus for applying a coating -to a surface of a work piece Whilesaid work piece is being rotated, comprising a movable supporting membermovable parallel to the axis of rotation of said Work piece, anelongated support member pivotally mounted on said movable means, anapplicator pivotally mounted on said elongated support at one endthereof, said applicator comprsing a drive roller and an applicatorroller rotatably coupled together and adapted to make peripheral contactwith the surface of said work piece, means for supplying a coatingmaterial to said applicator roller, and biasing means connected to theelongated support member for urging s-aid rollers against the surface ofsaid work piece.

References Cited in the le of this patent UNITED STATES PATENTS2,284,491 Mandell May 26, 1942 2,709,414 Powell et al May 3l, 19552,876,733 Bauman Mar. l0, 1959

1. APPARATUS FOR COATING A CYLINDRICAL SURFACE OF A WORK PIECECOMPRISING ROTATABLE MEANS ON WHICH SAID WORK PIECE CAN BE MOUNTED FORROTATION ABOUT THE AXIAL OF SAID CYLINDRICAL SURFACE, MEANS MOVABLERECTILINEARLY PARALLEL TO SAID AXIS, AN ELONGATED SUPPORT PIVOTALLYMOUNTED ON SAID MOVABLE MEANS WITH ONE END THEREOF EXTENDABLE AXIALLYALONG SAID CYLINDRICAL SURFACE WHEN SAID WORK PIECE IS MOUNTED ON SAIDROTATABLE MEANS, A PAINT APPLICATOR PIVOTALLY MOUNTED ON SAID ELONGATEDSUPPORT ADJACENT SAID ONE END THEREOF, SAID PAINT APPLICATOR COMPRISINGA SRIVE ROLLER AND A PAINT ROLLER ROTATABLY COUPLED TOGETHER ANDDISPOSED TO MAKE PERIPHERAL CONTACT WITH SAID TUBULAR SURFACE, AND MEANSFOR SUPPLYING PAINT TO SAID PAINT ROLLER.